For example, an atomic power plant including a pressurized water reactor (PWR) uses light water that is primary cooling water, as a reactor coolant and a neutron moderator, keeps the light water as high-temperature and high-pressure water that does not boil throughout an entire reactor internal, sends the high-temperature and high-pressure water to a steam generator to generate steam by heat exchange, and sends the steam to a turbine generator to generate power.
In such an atomic power plant, the pressurized water reactor needs to have periodic checks of various structures in order to secure sufficient safety and reliability. Then, when the checks are conducted and failure is found, a necessary place related to the failure is repaired. For example, in the pressurized water reactor, a reactor vessel main body is provided with a large number of instrumentation nozzles that penetrate a lower mirror. In each of the instrumentation nozzles, an in-core instrumentation guide tube is fixed to an in-core side upper end portion, and a conduit tube is connected to an ex-core side lower end portion. Further, a neutron flux detector that can measure a neutron flux can be inserted from the instrumentation nozzle to a reactor internal (fuel assembly) through the in-core instrumentation guide tube with the conduit tube. Further, the reactor vessel main body is provided with an output-side nozzle for supplying the primary cooling water to the steam generator, and an inlet-side nozzle for taking in the primary cooling water subjected to the heat exchange in the steam generator. A primary cooling water pipe, which communicates into the steam generator, is connected with these nozzles by welding. Since materials of the nozzles and the primary cooling water pipe are different, a safe end pipe is connected between the nozzles and the primary cooling water pipe by welding.
The instrumentation nozzle is configured such that an in-core instrumentation cylinder is fit into a mounting hole of the reactor vessel main body and is welded. Therefore, tensile stress may remain in the in-core instrumentation cylinder, a welded portion of the in-core instrumentation cylinder, and its peripheral portions, and a probability of occurrence of stress corrosion cracking becomes high due to long-term use. Further, tensile residual stress caused in the welded portion and its peripheral portion may also be a cause of the stress corrosion cracking in the inlet-side nozzle and the outlet-side nozzle. Therefore, conventionally, there is a water jet peening technology, in which tensile residual stress on a surface is improved into compressive residual stress, so that the stress corrosion cracking is prevented. The water jet peening is to jet high-pressure water containing cavitation bubbles to a surface of a metal member in water to improve the tensile residual stress on the surface of the metal member into the compressive residual stress. For example, Patent Literature 1 below discloses a technology that performs the water jet peening for the instrumentation nozzles.